The use of compounds containing the polymethylpiperidine group, and mainly 2,2,6,6-tetramethyl-1,2,2,6,6-pentamethylpiperidine, for the photostabilization of polymers is well known and to this end a wide literature exists.
Generally this class of stabilizing agents divided into two groups, namely those having low molecular weight (up to 500-600) and those with high molecular weight (higher than 600-700).
A detailed disclosure of some stabilizing agents of this class, the so called hindered amines, of their different kinds and of their applicative characteristic s found Gaechter-Mueller/Taschenbuch der Kunststoff-Additive, 2 Ausgabe 1983 pagg. 144-198.
U.S. Pat. Nos. 4,692,486 and 5,021,485 disclose some synergistic mixtures of derivatives of low and high molecular weight polyalkylpiperidines as photostabilizing agents for polymers. These mixtures contain some low molecular weight stabilizing agents included in the hereinafter described formula (I) together with high molecular weight stabilizing agents.
As disclosed in the above mentioned U.S. patents, these synergistic combinations show at the same concentration a photostabilizing activity remarkable better than the one of their single components.
A problem which is encountered in the polymer field is represented by their low resistance to oxidant agents, for example atmospheric oxygen. It is known in the art the use of sterically hindered phenols to stabilize polymers against oxidation.
The cited prior art gives no teaching about the antioxidant stabilization by the known photostabilizing agents.
It has surprisingly been found that new particular combinations of high and low molecular weight compounds containing the polymethylpiperidine moiety, in addition to synergistic properties as photostabilizing agents, also show synergistic activity in the long term heat stabilization of synthetic polymers. As used herein, the wording "long term heat stabilization" is intended to mean that the polymer is stabilized against the degradation which occurs during the time of use of the polymer itself.